1. Field of the Invention
The invention relates to a tank for storing a reducing agent.
2. Description of the Prior Art
The invention relates to a tank for storing a reducing agent as generically defined by the preamble to claim 1.
In internal combustion engines, especially diesel-fueled internal combustion engines, because of the more-stringent laws on exhaust gas expected in the next few years, among other things the proportion of nitrogen oxides in the exhaust gas must be reduced. For reducing of the proportion of nitrogen oxide in the exhaust gas, selective catalytic reduction is for instance performed, in which the nitrogen oxides are reduced with the aid of reducing agents to nitrogen and water. An aqueous urea solution, for instance, is used as the reducing agent.
The reducing agent is typically stored in a tank and fed via a line from the tank to a metering module, with which the reducing agent is injected for instance into the exhaust gas tube.
The usual reducing agents used at present, depending on the anti-freeze agent added, freeze at a temperature in the range from −11° C. to −40° C. If the demands in terms of the exhaust gas composition are to be met, it must be assured that even at temperatures below −11° C., reducing agent will be adequately available after an acceptable length of time. This makes it necessary under some circumstances to thaw out the reducing agent. In utility vehicles, for example, a connectable heater is used, which is operated via the engine coolant. This connectable heater is capable of thawing the contents of the entire tank.
However, since in passenger cars, for instance, the engine and the tank for the reducing agent are generally located far apart from one another, heating the tank for the reducing agent with the aid of the coolant of the engine is difficult. For this reason, in passenger cars, a limited volume of the tank, which is received in a partial container in the tank, is heated electrically. In tanks for the reducing agent that are in current use, it is possible to travel up to 1000 km with this thawed volume. In temperate climate zones, this thawed partial volume, in conjunction with the use of reducing agents with antifreeze additives is considered sufficient to assure uninterrupted operation. This also takes into account the fact that freezing the reducing agent in the tank in conjunction with purposeful insulation and intentional freezing can take several days.